Jops wrote:I've used a perspex shield before but only cos the amp was 2feet from the drums and mic'd. I imagine JB uses the perspex cos he records his live shows.
Isolation booths and/or baffles are used in a studio to prevent spill-over from various audio sources leaking into the mics on other instruments when recording in a 'live' band setting. Primarily used to isolate drum kit mics and sometimes the mics on various drums (baffle tunnel to separate spill into a kick drum mic) from others as it is an acoustic instrument source and subsequent balancing of levels in the mix can cause phase/comb filtering EQ effects as mic channels are combined.
The primary methods of achieving acoustic separation are to use absorptive and diffusive materials/methods in the construction of booths/baffles. Perspex is largely reflective, with minimal absorption and diffusion quality. I note that the engineer has put Auralex audio treatment on the bottom of the booth to control some of the reflections.
The use of perspex in live performance isolation is to attempt some separation of audio sources and therefore afford better mixing potential for broadcast or recording whilst allowing the audience to view the performer (drums) or other genre iconography (amp stacks).
This particular application would be problematic in that although the source mics may be shielded from the high stage SPL leakage from other sources, the performer would also be shielded from the direct sound/tone/volume source of the speakers for on stage monitoring purposes. What sound did bounce/reflect around and eventually find the ear of the guitarist would be coloured by the reflections/absorption/diffusion factors in the process so wouldn't be an accurate account of the direct sound.
Also mics (he has SM57s) are designed to accept audio from behind the diaphragm (that small mesh collar at the base of the capsule on a SM57) in a calculated phase relationship to the audio picked up in front of the diaphragm which combines at the diaphragm to colour the result in a pleasing aural way (hence the bass proximity effect renown of the SM57).
With a reflective shield so close to the back of the SM57, I'd be pretty sure (
) that the phase relationship between the direct sound and reflective sound would be an issue, for recording purposes, irrespective of the null lobes of the dynamic mic design and the close mic placement to the speaker cone.
The upshot being that this will cause as many problems as it would solve and would be a better fix if proper studio grade diffusion baffles were used or a separate speaker in an isolation box with a mic mounted inside, specifically tweaked for best colouration, was used off to the side out of audience view.